Spraying method and apparatus for powderless etching of printing plates



Aug. 15, 1961 E. J. DIRATS 2,995,851 SPRAYING METHOD AND APPARATUS FOR POWDERLESS ETCHING 0F PRINTING PLATES Filed July 6, 1959 3 Sheets-Sheet 1 [La/WY d. D/QArs BY Aug. 15, 1961 p -rs 2,995,851

SPRAYING METHOD AND APPARATUS FOR POWDERLESS ETCHING OF PRINTING PLATES Filed July 6. 1959 3 Sheets-Sheet 2 IN VEN TOR.

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United States Patent 13115 APPARATUS FOR row- DERLESS ETCHING OF PRINTING PLATES Elwyn J. Mass, assignor to J. Dirats & (30., Inc., Wesflield, Mass, a corporation of Massa- Filed July 6, 1959, Ser. No. 825,160 12 Claims. (Cl. 419) This invention relates to a method and apparatus for etching surfaces which have been provided in selected areas with an acid resistant coating; and more particularly to such apparatus designed for use with a so-called powderless" type etching liquid, such as the etching liquid disclosed in the pending application of Janik Dirats, Serial No. 718,090, filed February 27, 1958.

In this class of apparatus, a printing plate of magnesium, zinc, or appropriate alloy having a surface to be etched, is generally mounted face down in an etching tank above the level of etching liquid stored therein. Within the tank, beneath the plate, means such as rotating splash paddles serve to direct a spray of etching liquid against the face of the plate. Since it is desirable that the spray thus directed act uniformly over the face being etched, an intricate and relatively expensive mechanism is usually provided to give the plate a random translatory and rotational movement with respect to the liquid being sprayed against it. As the etching operation proceeds, cavities form in the face of the plate in the areas not protected by the resistant coating. If a powderless etching liquid is employed, a protective etch-resistant film builds up on the sides or shoulders of these cavities as they are formed. This protective film prevents the disadvantageous undercutting of the image areas by the continuous action of the etching liquid.

It has been found that the uniformity with which this protective film builds up on the cavity sides is affected by the flow pattern of the etching liquid impinging upon the plate. {When an etching liquid spray is directed at right angles to the surface being etched, as has often been the practice heretofore, the liquid impinging thereupon is broken into units which vary in size one from another. An irregular flow pattern is thus established which tends to build up a non-uniform protective film on the sides of the cavities formed in the etched surface. This frequently results in etched plates of unsatisfactory quality.

It is an object of the present invention to alleviate this undesirable situation by providing an etching procedure and etching means capable of reliably producing a more uniform protective film upon the sides of the cavities formed in an etched surface.

Toward this end, the improved apparatus provides for the subjection of the etched cavity sides to the etching fluid in such a way that each cavity side will at successive time intervals receive the direct impact of the liquid and will escape such impact in the interim periods. The nature of powderless etching liquid, and of its effect upon the metal being etched, is such that etching continues as long as there is a flow of liquid against and along a metal area, while etch-resistant film builds up, due to adsorption, in any area in which the flow pattern is momentarily discontinued.

More particularly, the improved procedure and apparatus involve the application of the etching liquid against the plate surface at a substantially single inclination thereto so that at any one time the liquid impinges directly only upon the cavity sides which are opposed to the direction of liquid flow and not upon the remaining sides. With respect to the latter sides, the flow pattern is thus discontinued during that period. The invention couples this angulated play of the liquid with a relative rotation between the plate and the directed stream of liquid where- Patented Aug. 15, 1961 by each cavity side or shoulder is subjected to alternate etch and rest periods. During the successive rest periods the desired film-building adsorption operation takes place.

The relative rotation of plate and liquid flow is preferably achieved by rotating the flow-directing means while the plate above it is held stationary or relatively so. This results in a great simplification of structure, as compared with mechanisms heretofore required to provide special or random plate movements.

In the preferred embodiment of the invention, the flowdirecting means comprises an array or manifold of apertured pipes or tubes, the tubes being arranged in parallel relation and the apertures in them being all disposed at substantially the same angularity with respect to the plate above. Power means is provided for rotating the manifold, and a pump supplies etching liquid to it in a continuous manner. Each emerging stream traces a frustoconical path with respect to the plate being etched.

Depending upon the pressure of the liquid, the angularity of its flow, and the vertical distance between the manifold and the plate, the axis of rotation of the manifold is preferably offset by a predetermined amount from the center, or approximate center, of the plate above it.

Other objects of the invention include provision of means for accurately controlling the intensity of the liquid fiow, means for heating or cooling the etchant as may be desired, and mans for maintaining the etching liquid in a constant state of emulsification.

Still other objects and advantages of the present invention will be apparent from the following description in which reference is made to the accompanying drawings.

In the drawings:

FIG. 1 is a perspective view of an etching apparatus constructed in accordance with this invention, shown open and showing its plate holding member in plate securing position;

FIG. 2 is a plan view of the apparatus with its cover closed;

FIG. 3 is a vertical cross-sectional view taken substantially on line 33 of FIG. 4;

FIG. 4 is a vertical cross-sectional view taken substantially on line 4-4 of FIG. 3;

FIG. 5 is a plan view of the liquid-directing'member or manifold;

FIGS. 6 and 7 are enlarged fragmentary detail views of the manifold, FIG. 7 being taken on line 77 of FIG. 6; and

FIG. 8 is a schematic view showing the relationship between the liquid directing means and a plate being etched.

Referring now to the drawings, an etching apparatus is shown comprising generally a tank 10 containing a quantity of etching liquid 11, a liftable cover 12 for closing the tank during etching, a holder 13 for supporting work to be etched, and a manifold 14 for directing the etching liquid upwardly against a plate supported in the holder 13. As may be seen in FIG. 1, the holder 13 is pivotally mounted about one edge thereof in order to permit the holder to be rotated upwardly into a substantially vertical position. In this position, a printing plate 15 or other element having a face 15a to be etched may be conveniently mounted in the holder 13 by means such as the clips 16, and thereafter the holder may be swung downwardly into a horizontal position, wherein the plate 15 will be supported face down in the tank 10 above the level of the etching liquid 11.

The etching liquid may be of any desired composition having the qualities necessary for the so-called powderless etching procedure. For example, the liquid may be of the general character described in the aforementioned pending application, Serial No. 718,090. Similarly, the plate to be etched may be of any desired composition suitable for co action with the etchant in the contemplated manner.

The liquid-directing manifold 14 is located below the horizontally disposed plate 15, and is preferably arranged parallel thereto. The manifold is fastened to a fluid tight rotary joint 19 which permits etching liquid to be fed to the manifold while the latter is rotated, the rotary motion being supplied through a bevel gear 20 fixed below the manifold 14. The detailed construction of the manifold will be apparent from an inspection of FIGS. 5, 6 and 7,wherein the manifold is shown comprising an elongated duct 21 and a plurality of crosswise tubular members 22. The duct is widest at its midpoint and tapers toward both ends in order to provide the largest flow area at its midpoint, and reduced flow areas toward the ends. The tubes 22 vary in length in inverse proportion to their distance from the midpoint of the duct. Preferably, the tubes are sized so as to create a circular liquid spray pattern whose center corresponds to the midpoint of the duct 21.

The duct is provided in its lower face with an opening 23 through which etching liquid enters the duct, and is provided in its upper face with a series of slots 24 through which the liquid enters the tubes 22. These tubes are disposed one over each of the slots 24. Each of the tubes is notched at its midpoint, the notches each having a depth approximately equal to the radius of the tube wherein it is located, and a length equal to the width of the duct at the point of attachment between the tube and the duct. In fabricating the manifold, the notched portion of each tube is fitted directly over the slot 24 in the duct 21 allocated to that tube, and the tube is fastened to the duct in fluid tight relation, as by welding.

The tubes 22 are each provided with a series of apertures 25 through which the liquid, which enters the manifold through the opening 23 in the duct 21, leaves the manifold in the form of a plurality of streams 26 directed against the face 15a of the plate 15 mounted in the holder 13. The intensity with which the streams of etching liquid strike the face 15a will naturally depend in part upon the pressure under which the liquid enters the duct 21.

The apertures 25 are so located in the tubes 22 that all the axes thereof are disposed at substantially the same predetermined angularity and direction with respect to the face of the plate 15. Furthermore, since the streams 26 are directed along the axes of the apertures 25, they strike the face 15a at an angle thereto. Thus, only the sides of the cavities in the face 15a which face into the direction of flow of the streams 26 will be subject to the direct impact of the liquid, while the remaining cavity sides will momentarily escape such impact. Of course, as the manifold 14 is rotated (see FIG. 8), all the cavity sides will be progressively subjected to the direct impact of the liquid streams 26 while the same sides will at other times escape the direct impact of the flow. Thus, all the sides of the cavities in the plate 15 are subjected to the same flow pattern, i.e., uniform streams of etching liquid strike all the cavity sides with the same intensity and for the same successive time periods, hence a uniform protective film builds up on the cavity sides during the interim non-flow or rest periods.

The manifold is supplied with etching liquid under pressure by a motor-driven pump 29 located outside the tank 10. The pump intake is located at the lowermost level of the tank 10, the latter being provided with a sloping bottom 30, and the pump delivers etching liquid through a conduit 31 and the rotary joint 19 into the duct 21 of the manifold. The liquid therefore, enters the manifold under a pressure determined by the speed of the pump.

Power for rotating the manifold 14 is furnished by a motor 32 located outside the etching tank 10. The motor supported within the tank. As shown, this shaft may 4 have a bevel gear, 34, on one end thereof disposed in meshing relationship with the bevel gear 20.

Referring to FIG. 5, it will be noticed that the axis of rotation R of the manifold is offset from the center C of the circular arrangement of tubes 22. This feature is present due to the fact that the liquid streams 26 follow a sloping path between the manifold and the plate 15. Therefore, in order to center the streams 26 with respect to the plate 15 at their points of contact with the plate, the center C is offset from the center of the plate. Further, in order to retain this centering of the streams during rotation of the manifold 14, the axis of rotation R is arranged to coincide with the center of the plate 15, hence the axis of rotation of the manifold and the center of the manifold are located at different points.

A shaft 35 running the length of the tank 10 is rotatably mounted adjacent its ends in the sides of the tank, and is provided along its length with a series of paddles 36 projecting outwardly therefrom. This shaft 35, when rotated, serves to agitate the etching liquid 11 contained in the tank to keep it in a constant state of emulsification. Power for rotating the shaft 35 is supplied by the motor 32, the power being transmitted to the shaft by a gear train 39.

The temperature of the etching liquid may be maintained at any desired level by the cooperation of strip heaters 40 and cooling coils 41 located near the bottom 30 of the tank 10. A control box 42 mounted on the out side of the tank contains instruments for controlling these heaters and cooling coils, and also for controlling the speed of the pump, the rotary speed of the manifold 14, and the agitator shaft 35.

The tank 10 may have upon its upper edge a flue 43 shaped to coincide with the contour of the tank. The inwardly facing walls of the flue 43 are provided with a number of slots 44 for the purpose of venting the etching liquid fumes from above the tank. The venting is accomplished by means of an exhaust fan 45 mounted on the outside of the tank.

While the invention is not restricted to apparatus of any specific dimensions, a better understanding of its general nature may be obtained by reference to the illustrative particulars which follow: The apertures in the manifold pipes may usually be between A and in diameter, spaced from A" to 1" apart; the angularity with respect to the vertical may be anywhere from approximately 7 to about 30; the space between the manifold and the plate above it may be from 1%" to about 6"; and where this spacing is 2%" (as is preferred) the angularity of the liquid streams may be about 13' from the vertical.

The invention has been shown and described in preferred form only, and it will be understood that many variations and modifications of the illustrated apparatus may be made by those skilled in the art without necessarily departing from the spirit and scope of the invention as expressed in the appended claims.

What is claimed is:

l. A method of etching the presensitized surface of a printing plate to form predetermined cavities therein, which consists in directing etching liquid against said surface at only a substantially single inclination thereto so that at any one time the liquid will impinge directly only upon the cavity sides which are opposed to the direction of liquid flow but will not impinge upon the remaining sides of said cavities, and causing relative rotation between the plate and the directed stream of liquid whereby each cavityside will at successive time intervals receive the direct impact of the liquid and will escape such impact in the interim periods.

2. A method of etching the presensitized surface of a printing plate to form predetermined cavities therein, which consists in directing etching liquid from a source said surface at only a substantially single inclination thereto so that at any one time the liquid will impinge directly only upon the cavity sides which are opposed to the direction of liquid flow but will not impinge upon the remaining sides of said cavities, and rotating said source whereby each cavity side will at successive time intervals rweive the direct impact of the liquid and will escape such impmt in the interim periods.

3. In an apparatus for etching printing plates, the combination of a plate holder, a manifold having an array of apertures therein, the axes of said apertures all being disposed at substantially the same predetermined angularity and direction with respect to a plate mounted in said holder, said angularity being at least about 7' from the perpendicular to the plate, means for providing relative circular motion between the plate and the manifold along an axis perpendicular to the plate, and pumping means iorldsupplying etching liquid under pressure to said mani- 4. The combination in accordance with claim 3, wherein said plate holder is arranged to support the plate face down in a srbstantially horizontal plane.

5. In an apparatus for etching printing plates, the combination of a plate holder, a manifold having an array of apertures therein, the axes of said aperturm all being disposed at substantially the same predetermined angularity and direction with respect to a plate mounted in said holder, said angularity being at least about 7 from the perpendicular to the plate, means for rotating said manifold along an axis perpendicular to the plate, and pumpmg means for supplying etching liquid under pressure to said manifold. 6. combination in accordance with claim 5 wherein said manifold comprises an elongated duct having a series of slots in one face thereof, and a plurality of tubular members mounted on said duct crosswise to the axis thereof, said members each being disposed over one of said slots and each having a series of said apertures running lengthwise thereof.

7. The combination in accordance with claim 6 wherein the cross-sectional area of said duct decreases gradually from its midpoint to its-ends, and said tubular members vary in length inversely with their distances from the midpoint of said duct whereby said members form a generally circular pattern whose center coincides with the midpoint of said duct.

8. The combination in accordance with claim 7 wherein 'said manifold-rotating means rotates said manifold about a point other than the mid-point of said duct.

9. In an apparatus for etching printing plates having a tank capable of holding a quantity of etching liquid, the combination within said tank of a plate holder whereon a printing plate is mounted face down during etching, a manifold comprising an elongated duct disposed below said plate holder and relatively close thereto, said duct being rotatably mounted about a vertical axis, and a plurality of tubes mounted upon said duct transversely thereto, each of said tubes having a longitudinal row of apertures in its wall, said apertures being positioned so that their axes are all disposed at substantially the same with respect to the face of a plate motmted in said holder, said angle being at least about 7 from the perpendicular to the plate a pump for transferring the etching liquid from said tank into said manifold thereby producing through said apertures in said tubes a plurality of streams of etching fluid which impinge along the axes of said apertures upon the face of a plate mounted in said holder, and means for rotating said manifold.

10. Apparatus in accordance with claim 9 wherein the axis of rotation of said manifold is offset with respect to the centere eof a plate mounted in said holder.

11. Apparatus in accordance with claim 10 wherein said tank is provided with a sloping floor, and the intake of said pump is located at the lowermost leevel in said 12 Apparatus in accordance with claim 11 including means for continuously agitating said liquid.

References Cited in the file of this patent UNITED STATES PATENTS 627,430 Levy June 20, 1899 964,126 Smith et a1 July 12, 1910 2,822,635 Meats Feb. 11, 1958 2,926,076 Guenst Feb. 23, 1960 

